1. Field of the Invention
The present invention relates to an optical scanning apparatus and an image forming apparatus using the optical scanning apparatus, and more specifically relates to an optical scanning apparatus in which a collimator lens and a cylindrical lens between a light source means and a light deflector are integrally configured to miniaturize and simplify the whole apparatus.
The present invention relates to an optical scanning apparatus suitable for a laser beam printer (LBP), a digital copying machine, a multifunction printer (multiple function printer), and the like employing an electrophotographic process, for example.
2. Related Background Art
Conventionally, in an optical scanning apparatus used for a laser beam printer, a digital copying machine, and the like, a light beam optically modulated and radiated from a light source means in accordance with an image signal is periodically deflected by a light deflector formed by a polygon mirror and the like, for example, and the light beam is condensed into a spot on a surface of a photosensitive recording medium by an imaging optical system configured by an fθ lens and the like, and the surface is optically scanned, thereby carrying out image recording.
FIG. 7 is a schematic diagram of a main portion of a conventional optical scanning apparatus of this kind.
In FIG. 7, a diverged light beam emitted from a light source means 91 is made to be a substantially parallel light beam or a converged light beam by a collimator lens 92, the light beam (light amount) is shaped by an aperture diaphragm 93, and the light beam is made incident upon a cylindrical lens 94 having a refractive power in a sub-scanning cross section only.
The light beam incident upon the cylindrical lens 94 is emitted as it is in a main scanning cross section. On the other hand, the light beam incident upon the cylindrical lens 94 is converged and imaged as a substantially linear image including a linear image in a vicinity of a deflecting surface 95a of a light deflector 95 configured by a rotary polygon mirror in the sub-scanning cross section.
The light beam reflected and deflected on the deflecting surface 95a of the light deflector 95 is guided onto a photosensitive drum surface 97 which is a surface to be scanned, via an imaging optical system (fθ lens system) 96 having an fθ characteristic.
The recording of image information is carried out by performing optical scanning on the photosensitive drum surface 97 in a direction of an arrow B (main scanning direction) by rotating the light deflector 95 in a direction of an arrow A.
Note that each element such as the collimator lens 92, the cylindrical lens 94, and the like constitutes one element of an incident optical system LA.
In recent years, with regard to the optical scanning apparatus and the image forming apparatus of this type, the demand for miniaturization and simplification (cost reduction) of the whole apparatus has increased.
In order to satisfy the demand, an apparatus in which the incident optical system having the collimator lens 92, the cylindrical lens 94, and the like, for example, is configured by one single anamorphic condenser lens (anisotropic refractive power single lens) (see U.S. Pat. No. 4,915,484).
In the U.S. Pat. No. 4,915,484, the simplification and the miniaturization of the apparatus are realized by forming the conventional incident optical system, which is configured by the collimator lens and the cylindrical lens, by one single anamorphic condenser lens.
Besides, a post-objective type imaging optical system using the anamorphic condenser lens (anisotropic refractive power single lens) capable of effecting functions of the collimator lens, two prisms, the cylindrical lens, and the like with one lens has been proposed (see Japanese Patent Application Laid-open No. H05-313089).
Japanese Patent Application Laid-open No. H05-313089 discloses the post-objective type imaging optical system in which a focal length in the main scanning cross section, in the whole optical system, is about ten times larger than the focal length in the sub-scanning cross section.
In Japanese Patent Application Laid-open No. H05-313089, the complex incident optical system structured by the collimator lens, two prisms, the cylindrical lens, and the like designed to prevent a decrease in the utilization efficiency of light is configured by one single anamorphic condenser lens, and by adapting the configuration of the anamorphic condenser lens as appropriate, it is possible to maintain the utilization efficiency of the light.
However, the anamorphic condenser lens as disclosed in U.S. Pat. No. 4,915,484 is configured by a glass-formed lens constituted by a glass lens. Accordingly, there is a problem in that the anamorphic condenser lens is difficult to manufacture (the cost is high) compared to a plastic-formed lens capable of being formed with short molding tact.
Just as the anamorphic condenser lens as disclosed in U.S. Pat. No. 4,915,484, the anamorphic condenser lens as disclosed in Japanese Patent Application Laid-open No. H05-313089 is configured by the optical glass, and therefore has a problem that it is difficult to manufacture.
Further, in U.S. Pat. No. 4,915,484 and Japanese Patent Application Laid-open No. H05-313089, adjustment (collimator adjustment) of degree of convergence (parallelism) of the light beam emitted from the anamorphic condenser lens is not disclosed.
Hereinbelow, an explanation is made as to the incident optical system configured by the conventional collimator lens and the cylindrical lens.
The incident optical system configured by the collimator lens and the cylindrical lens has a configuration such that the adjustment of the convergence degree (parallelism) of the light beam emitted from the incident optical system is carried out by moving the collimator lens in the main scanning cross section and by moving the cylindrical lens in the sub-scanning cross section in a direction of an optical axis.
That is, in the conventional optical scanning apparatus, it is possible to carry out the adjustments in the main scanning cross section and in the sub-scanning cross section, independently.
However, in the conventional optical scanning apparatus, there is a problem such that in a case where the collimator lens and the cylindrical lens are integrally configured, it is not possible to carry out the adjustments in the main scanning cross section and in the sub-scanning cross section, independently.
An object of the present invention is to provide an optical scanning apparatus that can be miniaturized and simplified as a whole, and an image forming apparatus using the same.